In this research, a prospective, multicenter(Tangdu Hospital of Fourth Military Medical University, Xi'an Gaoxin Hospital of Xi'an Medical College, Xianyang Central Hospital, Baoji Central Hospital, Xi'an Central Hospital, The First Hospital of Xi'an, The Fourth Hospital of Xi'an) open-label, follow-up clinical trial will carry out to evaluate the efficacy and safety of low-dose rituximab in treating NMOSD in Northwest China.

Neuromyelitis optica spectrum disorder (NMOSD) is a group of autoimmune inflammatory demyelinating disease of the central nervous system primarily characterized with recurrent optic neuritis and longitudinally extensive transverse myelitis, leading to blindness and paralysis. Incremental disability due to clinical attacks make it essential to prevent relapses with immunosuppressive therapy. Since the serological pathogenic marker anti-aquaporin 4 immunoglobulin G (anti-AQP4 IgG) has been identified, NMOSD has unveiled its autoimmune features with close connections to B cell-mediated humoral immunity. Rituximab, a chimeric monoclonal antibody directly against human CD20 molecular on the surface of B cells, has been reported to deplete peripheral CD20+ B cells and to be highly effective for treating NMOSD, and therefore been recommended as first-line therapy for this disorder. Unfortunately, there are still no consensus statements on dosing and follow-up regimens, which needs investigations to explore the efficacy and safety of different rituximab strategies. Previous studies have provided pilot evidence supporting the use of low-dose rituximab in preventing relapses in Chinese patients with NMO/NMOSD, however, prospective multicenter studies are still needed to determine the effectiveness of the modified strategy in treating NMOSD.

Inclusion Criteria:

Age between 16 and 75 years old;

Meet the 2007 or 2015 revised diagnostic criteria for NMOSD;

At least two relapses in recent two years and/or at least one attack or relapse in recent one years;

Expanded disability status scale (EDSS) score ≤7.0;

Willingness to sample collection, imaging study and other disease-related examinations and assessments;

Results of pregnancy tests for female patients with fertility during the screening period should be negative and effective contraception was used by the patient and her spouse during the study period;

Patients with informed consent.

Exclusion Criteria:

Other immunosuppressive agents are being used or have been discontinued for less than 3 months;

White blood cell count (WBC) <3 ×109/L, neutrophil count <1.5 ×109/L, hemoglobin (HGB) < 85 g/L, and platelet count (PLT) < 80×109/L;

Concomitant active liver disease or persistent elevation of transaminases more than three times above the normal upper limit;

Serious cardiovascular, kidney, blood and endocrine diseases, or history of malignant tumors, or severe infection;

Other chronic active immune diseases or stable conditions but requiring immunosuppressants or glucocorticoids, such as rheumatoid arthritis, scleroderma, Sjögren's syndrome, ulcerative colitis, AIDS, genetic or drug-induced immune deficiency;

Pregnant or lactating patients and those with family planning during the study period;

Allergy to rituximab and other components;

Inability to provide informed consent.